Correlation of Coexistent Charge Transfer States in F₄TCNQ-Doped P3HT with Microstructure

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Chemistry

Background:

• Understanding organic semiconductor (OSC) and dopant interactions in thin films is crucial for optimizing device performance.
• Doping efficiency in OSCs depends on chemical and electronic interactions between dopant and host materials.
• Existing models propose either integer charge transfer (ICT) or partial charge transfer (CPX) as doping mechanisms.

Purpose of the Study:

• To investigate the simultaneous presence and interplay of ICT and CPX states in doped OSC films.
• To elucidate the factors governing the charge transfer mechanism in OSC:dopant systems.
• To propose a refined model for charge transfer in doped OSCs based on experimental evidence.

Main Methods:

• Utilized a combination of spectroscopic techniques to probe electronic interactions.
• Analyzed F4TCNQ-doped P3HT films with varying microstructures (regioregular and regiorandom).
• Correlated spectroscopic observations with local energetic environments and microstructural characteristics.

Main Results:

• Demonstrated the simultaneous existence of both CPX and ICT states in F4TCNQ-doped P3HT films.
• Revealed that the nature of the charge transfer interaction is highly sensitive to the local energetic environment.
• Identified the electronic driving force, dictated by local microstructure, as the key determinant of the charge transfer mechanism.

Conclusions:

• The doping process in OSCs is not limited to a single mechanism but involves multiple pathways occurring concurrently.
• A multiphase model is proposed, where the local charge transfer mechanism (ICT or CPX) is determined by the local electronic driving force.
• Microstructure plays a critical role in defining the local energetic landscape and thus the charge transfer mechanism in doped OSCs.